Personal cleansing with mild surface-active cleansing bar preparations has become a focus of great interest. The processability of such bars has also become a focus of great interest. The smear properties of such bars have become a focus of even greater interest.
Some of the problems associated with mild bars comprised of synthetic detergents are bar processability, firmness, smear and mildness. The problems of formulating such bars are not limited to the performance characteristics of the finished bars. Most bars which are made with certain mild surfactants are very difficult to fabricate.
In contrast, the fabrication of relatively pure "soap" bars is a well-worked-out engineering procedure involving milling, plodding and molding. Coco/tallow soap becomes quite plastic when warmed and can be easily plodded and molded under relatively low pressures.
Most synthetic detergents and detergent-filler combinations do not become plastic and the machinery for fabrication must be specially designed. See U.S. Pat. No. 2,678,921, J. A. V. Turck, Jr., issued May 18, 1954.
Ideal processing should be fast and problem free in terms of milling, plodding and molding toilet bar formation. Most mild bar processings fall short in this respect.
The development of soap-synthetic bars dates back to World War II. U.S. Pat. No. 2,432,169, Hoyt, describes a bar having soap and alkyl benzene sulfonate as the active and a substantial proportion of corn starch as a binder; and U.S. Pat. No. 2,988,511, Mills and Korpi, issued Jun. 13, 1961, describes a nonsmearing bar comprising alkyl glyceryl ether sulfonate, sodium and magnesium soaps and binder. U.S. Pat. No. 2,982,735, Blinka and Grounds, Jr, issued May 2, 1961, discloses a detergent milled bar comprising soap, anionic detergent and starch.
U.S. Pat. No. 2,781,321, Mayhew et al., issued Feb. 12, 1957, discloses (Example 19) a 50% Mg stearate all purpose detergent bar with 20% gum, etc. The surfactant system includes dodecylbenzene sulfonate in Examples 26-30, which is a relatively harsh surfactant. STPP is used at levels of 10-15% in Mayhew et al.'s examples.
U.S. Pat. No. 3,070,547, Charfee, issued Dec. 25, 1962, also discloses a potassium synthetic soap-synthetic bar containing magnesium soap. There appears to be no free fatty acid in the Chaffee exemplified bars, and the pH's of his surfactant systems used in those examples are not disclosed, but are normally relatively high.
U.S. Pat. No. 2,987,484, Lundberg and Blinka, issued Jun. 6, 1961, discloses a closed die injection molded detergent bar comprising alkyl glyceryl ether sulfonate and acyl isethionate. Some other uses and procedures for making alkyl glyceryl ether sulfonate are disclosed in U.S. Pat. No.: 2,094,489, Hulter, issued Sep. 28, 1937; U.S. Pat. No. 2,427,576, Smith, issued Sep. 16, 1947; U.S. Pat. No. 2,427,577, Smith, issued Sep. 16, 1947; U.S. Pat. No. 2,989,547, Whyte, issued Jun. 20, 1961; U.S. Pat. No. 2,999,068, Pilcher et al., issued Sep. 5, 1961; and U.S. Pat. No. 3,024,273, Whyte et al., issued Mar. 6, 1962, all of said patents incorporated herein by reference.
It is noted that surfactant mildness can be measured by a skin barrier destruction test which is used to assess the irritancy potential of surfactants. In this test the milder the surfactant, the less the skin barrier is destroyed. Skin barrier destruction is measured by the relative amount of radio-labeled water (.sup.3 H--H.sub.2 O) which passes from the test solution through the skin epidermis into the physiological buffer contained in the diffusate chamber. This test is described by T. J. Franz in the J. Invest. Dermatol., 1975, 64, pp. 190-195; in U.S. Pat. No. 4,673,525, Small et al., issued Jun. 16, 1987, and in copending U.S. patent application Ser. No. 294,832, Small et al., filed Jan. 9, 1989, incorporated herein by reference.
U.S. Pat. No. 2,894,912, Geitz, issued Jul. 14, 1959, for "Isethionate Detergent Bar," discloses a detergent bar consisting essentially of from 30-70% of water-soluble alkali metal detergent salts of esters of isethionic acid with mixed aliphatic fatty acids having from 6 to 18 carbon atoms and an iodine value of less than 20, of which mixed acids at least 75% have from 12 to 18 carbon atoms and up to 25% have from 6 to 10 carbon atoms, from 2-10% of at least one water-soluble suds-boosting detergent salt selected from the group consisting of alkali metal and organic amine higher aliphatic fatty alcohol sulfates, alkyl aryl sulfonates, and higher aliphatic fatty acid taurides, from about 1% to about 9% water, from about 2.5% to about 25% of water-soluble higher fatty acid soap, and from 10-40% of at least one higher fatty acid having from about 12 to about 25 carbon atoms as a binder and plasticizer, said bar having a pH within the range from 6 to 8, measured as a 10% aqueous solution of the bar composition at 35.degree. C. No magnesium soap is used.
U.S. Pat. No. 4,180,470, Tokosh et al., issued Dec. 25, 1979, discloses a method for making improved 30-70% acyl isethionate detergent bars with from 2-6% of sodium alkoxy hydroxy propane sulfonate (a synonym for alkyl glyceryl ether sulfonate) with alkyl chains of from 8 to 22 carbon atoms in conjunction with a small amount of sodium chloride. C.sub.18 alkyl glyceryl ether sulfonate at 5% is used in an example. The added alkyl glyceryl ether sulfonate and salt are used to improve bar wear rate without adversely affecting its lathering characteristics.
U.S. Pat. No. 4,234,464, Morshauser, issued Nov. 18, 1980, for "Detergent Bar Composition and Binder Therefor," discloses a detergent bar in Example 6 which comprises: 45% sodium cocoyl isethionate, 5% alkyl amide, 37.5% stearic acid, 5.0% hydrogenated tallow glycerides, and 1% Polymer JR. Morshauser teaches that his detergent bars can contain up to 5% soap "without substantial detriment."
U.S. Pat. No. 4,012,341, Orshitzer et al., issued Mar. 15, 1977, for a "Unique All Synthetic Detergent Shampoo Bar," discloses a bar comprising a mixture of anionic and nonionic detergents. The Examples are primarily based on sodium lauryl sulfate, which is an unacceptably harsh primary surfactant for the present invention.
U.S. Pat. No. 3,761,418, Parran, Jr., issued Sep. 25, 1973, for "Detergent Compositions Containing Particle Deposition Enhancing Agents," discloses detergent compositions including a bar, whose main surfactant is alkyl sulfate, which is unacceptable for the mild skin cleanser of the present invention.
Major drawbacks of most synthetic surfactant toilet bar formulations are harshness, poor lather, poor smear, and poor processability due to stickiness. The use of high sudsing anionic surfactants can yield acceptable lather volume. Unfortunately, the highest sudsing anionic surfactants are, in fact, poor in processability. While some prior art mild blends of sodium coconut/tallow alkyl glyceryl ether sulfonate (AGS) are relatively good in lather potential, they are not so easy to process because of their stickiness or hygroscopicity. It will be appreciated that processability, firmness, smear, mildness, lather, and rinsability make surfactant selection for mild personal cleansing bars a delicate balancing act. Thus, it will be appreciated that rather stringent requirements for formulating mild personal cleansing bars limit the choice of surfactants, and final formulations represent some degree of compromise. Mildness is often obtained at the expense of processability, effective cleansing, lathering, or rinsing, or vice versa. Processability is often obtained at the expense of smear.
Needless to say, a superior processable mild personal cleansing bar formulation with good mildness, good smear, good lather potential and good rinsability is difficult to formulate.